The present invention relates to a plasma processing technique, and in particular, to a plasma processing technique to monitor a monitor value of a monitor attached to a plasma processing apparatus to thereby detect an abnormality of the apparatus in an early stage of the abnormality.
For plasma processing apparatuses used to produce semiconductor products, in association with fine manufacturing of devices, high integration thereof, variety of materials of the products; importance is attached not only to uniformity of processing and improvement of precision, but also to mass-productivity such as long-term stability of processing characteristics and suppression of discrepancy of processing between a plurality of plasma processing apparatuses. Therefore, in one and the same chamber, it is required to keep the plasma characteristics fixed for a long period of time. Also when some worn parts are replaced at maintenance of the plasma processing apparatuses, the plasma characteristics are required to be kept unchanged. When a plurality of chambers are employed, it is required in the management thereof to detect fine characteristic difference between the chambers to correct the difference.
When a plasma etching apparatus is used for a long period of time, an inner wall of its chamber is worn or deposited substance is accumulated on the inner wall. This resultantly changes the process environments such as reaction on a surface of the inner wall of the chamber and an electric characteristic of the plasma. When the change in the process environments proceeds, the fine patterning characteristic is beyond its range of allowance at a certain point of time. For example, the gate dimension of a device is beyond the allowance range, and the produced Large Scale Integration (LSI) device is deteriorated in performance as a result. Furthermore, if the deposition of substance on the inner wall proceeds, the deposited substance peels off as dust particles from the inner wall and causes an etching defect.
On the other hand, wearing of parts such as the inner wall also causes abnormal discharge at a certain point of time to abruptly increase deteriorated substance, which possibly becomes a factor to fatally increase the failure ratio. In some cases, in addition to the simple wearing of the inner wall of the chamber, there occurs peeling of a coating film formed on the inner wall to enhance strength against the plasma. Or, breakdown of insulation possibly takes place in the coating film. If a part replaced at maintenance or its assembled state is defective, a change appears in the processing characteristics.
To avoid such an event in which processing characteristics are beyond the range of allowance, various measures have been taken in recent plasma processing apparatuses. For example, various monitor values such as an emission spectrum, a peak-to-peak voltage value Vpp of the bias waveform, and the behavior of the reflected wave are continuously monitored to thereby determine whether or not the mass-production can be continuously conducted. Or, new material having higher strength is used for the inner wall to prevent the wearing thereof. Additionally, development of techniques is underway, for example, a technique in which the processing is stopped before occurrence of the processing failure and a technique to elongate the processing time lapsed up to a point of time of occurrence of the processing failure.
However, in a case in which the condition of the plasma processing apparatus is monitored using various monitor values, even if a monitor value changes and a change of the condition relative to an associated normal condition is confirmed, the cause of the change cannot be determined in some cases. For example, it is not possible to determine a part having caused the change in the monitor value and the resultant condition of the apparatus associated with the change.
In such a case, unnecessary maintenance is inevitably carried out depending on the case. For example, the chamber is disassembled and is entirely cleaned or some parts not to be necessarily and inherently replaced are replaced to guarantee operation of the plasma processing apparatus. This lowers the availability ratio of the apparatus and increases the cost for worn parts. Only if parts causing changes in monitor values and/or the abnormality can be determined, it is possible to beforehand prepare associated parts to be replaced in the maintenance.
Therefore, in addition to an operation to simply monitor a fine change in the process environments in the chamber generating the plasma and a trifle difference between the plasma processing apparatuses, there is required an operation to classify and determine a part causing the detected change or abnormality and a condition of the apparatus associated with the change or abnormality. This makes it possible to beforehand predict parts to be replaced.
The known monitor values to be monitored to determine the state of the plasma processing apparatus include the reflected wave power of the plasma generating electromagnetic wave, the light emission spectrum of the generated plasma, the peak-to-peak value Vpp of the bias voltage waveform applied to the wafer, and the matching point of the matching device of the plasma generating power source or the bias applying power source. Description will now be given of a technique to monitor the process progress state by use of these monitor values, specifically, a technique to monitor a condition change in the plasma generating chamber.
JP-A-2003-282542 describes a technique of determining, in a plasma processing apparatus of a method of using one frequency for the high-frequency wave to generate plasma and the high-frequency wave to apply the bias voltage, presence or absence of an abnormality in the plasma processing by monitoring a high-frequency current applied from the side of a sample processing stage (referred to as “sample stage” hereunder) to thereby compare the current value of the current with a high-frequency current value in the normal state.
JP-A-2003-282545 describes a technique of determining, in a plasma processing apparatus of a method of using one frequency for the high-frequency wave to generate plasma and the high-frequency wave to apply the bias voltage, presence or absence of abnormal discharge in the chamber on the basis of a fact that a change on the side of the plasma as the object of control operation can be detected using a monitor voltage sense by a matching circuit on the side of the sample stage. However, in this technique, neither the kind of abnormality nor the position of occurrence thereof is determined.